Canadian Security Intelligence Service (CSIS) director Michel Coulombe waits to testify before the Senate national security and defence committee in Ottawa February 3, 2014.

Reuters/Chris Wattie

TORONTO Canadians who go abroad to join militant groups such as Islamic State pose a threat on their return home and could use their foreign contacts to set up networks in Canada, the country's intelligence director said on Saturday.

Michel Coulombe, director of the Canadian Security Intelligence Service, wrote in a Globe and Mail article that "well over 100 Canadians," both men and women, have left the country to join groups such as al-Qaeda and al-Shabaab.

"The most obvious national-security threat is the one posed by extremists who return," Coulombe said. "How many are coming back to Canada more radicalized than when they departed? Will their status as veterans of a foreign conflict better enable them to recruit other Canadians?

"And, most importantly, will they use their terrorist training to attempt violent acts here in Canada? This is a very real prospect."

Other Western governments have expressed similar concerns about citizens who go abroad to join militants fighting in the Middle East and elsewhere and then return home radicalized. Islamic State militants now control swathes of Iraq and Syria.

Britain announced plans on Saturday to crack down further on such militants. On Friday, Austria raised its estimate for the number of residents suspected of allying themselves with militants fighting abroad.

Last month, a Canadian provincial court imposed a 10-year prison sentence on a man convicted of attempting to join a militant group abroad.

The conviction comes as Canada wrestles with several cases of radicalized Canadians plotting attacks at home or heading overseas to join militant groups. Two men were arrested last year and charged with plotting to derail a Toronto-area passenger train bound for New York.

Also last year, two Canadians were part of a group that stormed a gas plant in Algeria and took hostages. After a four-day siege, Algerian forces stormed the plant. At least 80 people were killed.

Coulombe said some of those who went abroad had been killed, including the two in Algeria "and a number of other young men from Calgary who met a violent end in Syria or Iraq".

"Even if a Canadian extremist does not immediately return, he or she is still a Canadian problem," Coulombe said. "No country can become an unwitting exporter of terrorism without suffering damage to its international image and relations."